1. Field of the Invention
This invention relates to a laser scanning apparatus suitable for use on a laser printer or the like.
2. Description of the Prior Art
In the art of laser scanning apparatus, it has been the usual practice to deflect a laser beam by means of a rotary polygonal mirror, thereby scanning a photosensitive medium with the laser beam after correcting its focal point according to the deflection angle through a correction lens. For example, Japanese Patent Laid-Open No. 46713/1989 describes a laser scanning apparatus of this sort employing a correction lens which is formed by linearly cutting off upper and lower portions of a circular lens in such a manner as to provided parallel upper and lower faces on the opposite sides of the optical axis of the lens. The lower face of the correction lens, serving as a mounting surface, is held in intimate contact with a base plate which has a lens positioning means projectingly provided thereon, and a resilient lid member is fitted over the upper face of the correction lens and fittingly engaged with the positioning means. A projection formed on the resilient lid member is abutted against the upper marginal edge of the correction lens to push the same against the base plate and the positioning means, thereby holding the lens fixedly in position.
Generally, at the time of mounting a correction lens on a laser scanning apparatus, high accuracy is required with regard to the position of the optical axis of the lens. However, in the conventional laser scanning apparatus in which the position of the optical axis is determined on the basis of the mounting surface formed by a lens cutting operation, high accuracy is required not only with respect to the base plate and the positioning member but also on the mounting surface of the correction lens. It follows that the mounting surface needs high precision cutting and machining operations which lengthen and complicate the lens machining process and considerably increase production costs.